:root {
  --bg: #f5efe4;
  --bg-soft: #fffaf2;
  --ink: #1f2933;
  --muted: #5d6975;
  --line: rgba(31, 41, 51, 0.12);
  --primary: #0f766e;
  --primary-strong: #115e59;
  --accent: #e76f51;
  --card: rgba(255, 250, 242, 0.82);
  --shadow: 0 18px 40px rgba(31, 41, 51, 0.12);
  --radius: 24px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: "IBM Plex Sans", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(15, 118, 110, 0.22), transparent 28%),
    radial-gradient(circle at top right, rgba(231, 111, 81, 0.18), transparent 24%),
    linear-gradient(180deg, #f6f1e7 0%, #f3e8d8 100%);
}

a {
  color: inherit;
}

.page-shell {
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  padding: 24px 0 64px;
}

.top-nav {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 18px;
}

.top-nav a {
  padding: 10px 14px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.56);
  text-decoration: none;
  border: 1px solid var(--line);
}

.hero,
.page-hero,
.card,
.section-highlight {
  backdrop-filter: blur(10px);
}

.hero {
  display: grid;
  grid-template-columns: 1.4fr 0.9fr;
  gap: 24px;
  padding: 32px;
  border: 1px solid var(--line);
  border-radius: 32px;
  background: rgba(255, 248, 238, 0.72);
  box-shadow: var(--shadow);
}

.page-hero {
  padding: 28px;
  border: 1px solid var(--line);
  border-radius: 32px;
  background: rgba(255, 248, 238, 0.72);
  box-shadow: var(--shadow);
}

.eyebrow {
  margin: 0 0 12px;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--primary);
}

h1,
h2,
h3 {
  font-family: "Space Grotesk", sans-serif;
  margin: 0;
}

h1 {
  font-size: clamp(2.4rem, 5vw, 4.3rem);
  line-height: 0.98;
  max-width: 12ch;
}

h2 {
  font-size: clamp(1.8rem, 3vw, 2.6rem);
  margin-bottom: 8px;
}

h3 {
  font-size: 1.3rem;
  margin-bottom: 10px;
}

p {
  color: var(--muted);
  line-height: 1.65;
}

/* Keep MathJax content inside cards on small screens */
mjx-container[jax="CHTML"] {
  max-width: 100%;
}

p mjx-container[jax="CHTML"],
li mjx-container[jax="CHTML"],
.property-item mjx-container[jax="CHTML"],
.set-item mjx-container[jax="CHTML"] {
  display: inline-block;
  vertical-align: middle;
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
}

mjx-container[jax="CHTML"][display="true"] {
  display: block;
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
  padding-bottom: 4px;
}

.hero-text {
  max-width: 58ch;
}

.hero-actions,
.equivalence-actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  border: 1px solid transparent;
  padding: 12px 18px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: transform 0.18s ease, background 0.18s ease;
}

.button:hover {
  transform: translateY(-1px);
}

.button-primary {
  background: var(--primary);
  color: #fff;
}

.button-primary:hover {
  background: var(--primary-strong);
}

.button-secondary {
  background: rgba(255, 255, 255, 0.56);
  color: var(--ink);
  border-color: var(--line);
}

.button.small,
.pill {
  padding: 10px 14px;
}

.full {
  width: 100%;
  margin-top: 12px;
}

.pill {
  display: inline-flex;
  margin-top: 12px;
  border-radius: 999px;
  background: rgba(231, 111, 81, 0.14);
  color: var(--accent);
  font-weight: 700;
}

.hero-panel {
  display: grid;
  gap: 16px;
}

.stat-card,
.card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--card);
  box-shadow: var(--shadow);
}

.stat-card {
  padding: 20px;
}

.stat-card strong {
  display: block;
  margin-top: 8px;
  font-size: 1.4rem;
  font-family: "Space Grotesk", sans-serif;
}

.stat-card.accent {
  background: linear-gradient(135deg, rgba(231, 111, 81, 0.18), rgba(255, 250, 242, 0.9));
}

.stat-label {
  color: var(--muted);
  font-size: 0.9rem;
}

.section {
  margin-top: 28px;
}

.section-heading {
  margin-bottom: 18px;
}

.topic-grid,
.recommendation-grid,
.fraction-layout,
.page-grid,
.info-grid {
  display: grid;
  gap: 18px;
}

.topic-grid {
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
}

.fraction-layout,
.page-grid {
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  margin-top: 18px;
}

.info-grid {
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
}

.set-list,
.property-list {
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-top: 18px;
}

.span-2 {
  grid-column: span 2;
}

.card,
.section-highlight {
  padding: 24px;
}

.section-highlight {
  border: 1px solid var(--line);
  border-radius: 32px;
  background: rgba(255, 248, 240, 0.74);
  box-shadow: var(--shadow);
}

.subtopics {
  margin: 14px 0 0;
  padding: 0;
  list-style: none;
}

.subtopics li,
.info-item {
  padding: 10px 12px;
  margin-top: 10px;
  border-radius: 16px;
  background: rgba(15, 118, 110, 0.06);
  color: var(--ink);
}

.set-item,
.property-item {
  padding: 16px 18px;
  border-radius: 18px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.68);
}

.set-item h4,
.property-item h4 {
  margin: 0 0 10px;
  font-family: "Space Grotesk", sans-serif;
  font-size: 1.05rem;
}

.set-item p,
.property-item p {
  margin: 8px 0 0;
}

.fraction-visual-card {
  display: flex;
  gap: 18px;
  align-items: center;
  flex-wrap: wrap;
  margin-top: 18px;
  padding: 18px;
  border-radius: 18px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.68);
}

.fraction-bar-demo {
  display: grid;
  grid-template-columns: repeat(4, minmax(42px, 1fr));
  gap: 6px;
  width: min(320px, 100%);
}

.fraction-bar-demo.six {
  grid-template-columns: repeat(6, minmax(32px, 1fr));
}

.bar-piece {
  min-height: 64px;
  border-radius: 12px;
  border: 1px solid rgba(15, 118, 110, 0.22);
  background: rgba(15, 118, 110, 0.08);
}

.bar-piece.filled {
  background: linear-gradient(180deg, #1f9d8d 0%, var(--primary) 100%);
}

.fraction-math strong {
  display: block;
  font-family: "Space Grotesk", sans-serif;
  font-size: 2rem;
}

.fraction-math p {
  margin: 8px 0 0;
}

.mixed-visual {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.whole-block {
  width: 84px;
  height: 84px;
  border-radius: 16px;
  border: 1px solid rgba(15, 118, 110, 0.22);
  background: rgba(15, 118, 110, 0.08);
}

.filled-whole {
  background: linear-gradient(180deg, #1f9d8d 0%, var(--primary) 100%);
}

.whole-block.thirds {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 4px;
  padding: 4px;
}

.whole-block.thirds span {
  border-radius: 10px;
  background: rgba(15, 118, 110, 0.08);
}

.whole-block.thirds .filled-third {
  background: linear-gradient(180deg, #1f9d8d 0%, var(--primary) 100%);
}

.fraction-stack {
  margin-top: 18px;
}

.equivalence-visual {
  display: flex;
  flex-direction: column;
  gap: 14px;
  width: min(420px, 100%);
}

.equivalence-row {
  display: flex;
  gap: 14px;
  align-items: center;
  flex-wrap: wrap;
}

.bar-piece.wide {
  min-width: 64px;
}

.controls {
  display: grid;
  gap: 14px;
  margin: 16px 0;
}

label {
  display: grid;
  gap: 8px;
  font-weight: 600;
}

input[type="range"],
input[type="number"],
select {
  width: 100%;
}

input[type="number"],
select {
  padding: 10px 12px;
  border-radius: 14px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.82);
  font: inherit;
}

.fraction-bar {
  display: grid;
  grid-template-columns: repeat(var(--segments, 4), 1fr);
  gap: 6px;
  min-height: 64px;
  margin: 18px 0 14px;
}

.fraction-segment {
  border-radius: 12px;
  border: 1px solid rgba(15, 118, 110, 0.22);
  background: rgba(15, 118, 110, 0.08);
}

.fraction-segment.filled {
  background: linear-gradient(180deg, #1f9d8d 0%, var(--primary) 100%);
}

.fraction-summary {
  display: flex;
  align-items: baseline;
  gap: 14px;
  flex-wrap: wrap;
}

.fraction-summary strong,
.equivalence-main span {
  font-family: "Space Grotesk", sans-serif;
  font-size: 2rem;
}

.equivalence-box {
  display: grid;
  gap: 16px;
}

.equivalence-main small {
  display: block;
  color: var(--muted);
}

.equivalence-result,
.result-box,
.error-card,
.exercise-prompt {
  padding: 14px 16px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--line);
}

.exercise-prompt {
  font-family: "Space Grotesk", sans-serif;
  font-size: 2rem;
  text-align: center;
}

.operation-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 14px;
  margin-bottom: 18px;
}

.fraction-inputs {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 8px;
  align-items: center;
}

.error-options {
  display: grid;
  gap: 10px;
  margin: 16px 0;
}

.error-option {
  text-align: left;
}

.compact {
  min-height: 72px;
}

@media (max-width: 900px) {
  .hero {
    grid-template-columns: 1fr;
  }

  .span-2 {
    grid-column: auto;
  }
}

@media (max-width: 640px) {
  .page-shell {
    width: min(100% - 20px, 1180px);
    padding-top: 20px;
  }

  .hero,
  .page-hero,
  .card,
  .section-highlight {
    padding: 20px;
    border-radius: 24px;
  }

  h1 {
    font-size: 2.3rem;
  }

  .page-grid,
  .fraction-layout {
    grid-template-columns: 1fr;
  }

  .property-item,
  .set-item,
  .card {
    min-width: 0;
  }

  p mjx-container[jax="CHTML"],
  li mjx-container[jax="CHTML"],
  .property-item mjx-container[jax="CHTML"],
  .set-item mjx-container[jax="CHTML"] {
    font-size: 0.92em !important;
  }

  mjx-container[jax="CHTML"][display="true"] {
    font-size: 0.92em !important;
  }
}